FIG. 1 shows a prior art optical combiner 100 using a diode laser array 102, which provides a linear array of diode lasers on a single plane, typically with regular spacing (pitch) between each laser emitter 104a, 104b, etc. Each diode laser such as 104a is coupled using a refractive lens 108a to focus emitted optical energy into the core of a corresponding optical fiber 110a, and the multiple optical fibers are typically arranged in a circular packed arrangement at an output end 120, with an example of the fiber 110a circular packing of detail B-B as shown in FIG. 1B for 7 diode array 102 emitters coupled into the 7 fibers 110a-110g as shown. Because of this prior art use for coupling the output of a diode laser array into a circularly packed pattern (known as a hexagonal lattice in circle packing theory), the number of emitters on diode laser array 102 is typically set at the hexagonal lattice number N, where N=7, N=19, N=37, etc to achieve an optimal circular packing arrangement.
FIG. 1 also shows a detail region 106 which is presented in FIG. 1A detail A-A, showing diode laser array 102, individual laser emitters 104a and 104b of the array, each of which has a diverging optical output 109a, which is focused by corresponding lens 108a to the converging optical energy 111a from the output of the lens to the central core of optical fiber 110a, which guides the optical energy to the output end 120 of each optical fiber. The core 112a of one example optical fiber is shown with respect to optical fiber 110a in FIG. 1B.
It is also clear from FIG. 1B that, since the optical energy is only carried in the core such as 112a of each optical fiber such as 110a, the overall carried energy density from the plurality of diode laser outputs is reduced by this arrangement. A typical multimode optical fiber for high power applications has a core diameter of 200 μm which carries the optical energy, and a surrounding cladding diameter of 220 μm which guides the optical energy, and an outer jacket (not shown) which must be stripped to provide reasonable packing density limited by the cladding diameter. Assuming that each diode laser has 1 W output energy, the optical power density coupled to the core at the input of each optical fiber is 3183 W/cm2 presuming focused beam size equal to the fiber core size. It is instructive to compare the power density coupled into the optical fiber with the power density coupled out of it as shown in FIG. 1B, where in our example (for a lossless system) 7 W of optical energy in a 660 um diameter circle (governed by the cladding diameter in our example), for an energy density of 2046 W/cm2. The reduction in energy density is the result of the inefficient combining, since only the optical fiber core carries optical energy, not the inactive or unused areas within the output fiber bundle packing. Additionally, the precise alignment of each lens 108a and associated emitter 104a to assure only the fiber core is fully illuminated is problematic and difficult to manufacture in a repeatable manner, and also is subject to thermal and mechanical effects. Furthermore, manipulation and bundling of discrete optical fibers further complicates production fabrication processes, and optical energy reflected from the air/fiber interface which couples back to the laser disrupts the cavity operation of the diode laser and may result in instability or catastrophic failure of the high power laser emitter. Another difficulty is that the use of micro lenses such as 108 could cause surface reflection of optical energy back to the diode laser emitter, resulting in instability of the high Q diode laser cavity.
A simplified optical combiner is desired which provides the capability for combining optical energy from a diode laser array and without the counter propagating reflections of micro lenses 108a such that minimal optical energy is reflected back to the diode laser, and which utilizes waveguide channels to provide the function of combining optical power from each of several diode laser outputs to a single combined optical output of the optical combiner.